1. Field of the Invention
This invention relates to lens holding barrels made of plastic material by unified molding techniques.
2. Description of the Prior Art
Molded plastic barrels for lenses have already been known as, for example, in Japanese Laid-Open Utility Model Application No. SHO 59-90906. As shown in FIGS. 1 and 2, the lens barrel 1 has two protuberances 1b and 1c on the inner surface 1a thereof. A plurality of lenses L in the barrel 1 are thrusted to one radial direction. Hence, although the optical axes of the lenses are less deviated from one another, they are off-set to the ideal axis of the barrel by about the radial height of the protuberance 1b, 1c. Since the inner diameter of the barrel is necessarily slightly larger than the outer diameter of the lens, such a decentering is difficult to avoid.
As another conventional example, mention may be made of the lens cell shown in Japanse Laid-Open Utility Model Application No. SHO 57-167408. This cell is formed by a metal mold and has three protuberances on the inner surface thereof.
By the way, in the former conventional example, the position of the optical axis of the lens is determined by the two protuberances 1b and 1c and a point of contact of the lens with the inner surface of the barrel 1a. Since, as the barrel 1a and the protuberances 1b and 1c are formed by a single metal mold, the optical axis of the lens is made to approach the ideal axis of the barrel, or a molding error is removed, there is only one freedom of correction of the metal mold in the direction indicated by an arrow in FIG. 1. Therefore, the problem of decentering the optical axis of the lens has been left unsolved.
In the latter conventional example, the diameter of a circle passing the tips of the three protuberances had to be larger than the diameter of the lens by machining tolerances. As the lens was loosely fitted in the barrel in most cases, there was a drawback that no means was provided for absorbing that looseness.